Under the agreement, RDF founder and chief executive David Frank has been appointed to the same position in Zodiak Entertainment.
Lorenzo Pellicioli, chief executive of Zodiak-owner De Agostini Group and chairman and chief executive of Zodiak, will now serve as chairman of the new enlarged group.
The RDF deal will mean that Zodiak has a "significant presence" in over 20 countries, including the UK, the US, France, Italy, Spain, Scandinavia and Russia.
"With the acquisition of RDF Media Group the consolidation process of Zodiak is completed," said Pellicioli.
"Zodiak, with its strong international footprint and its presence in all entertainment formats, is today one of the main content producers in the world.
"We are particularly glad to welcome David Frank as the new future CEO of Zodiak and we are sure that his experience and his deep expertise will lead Zodiak towards important goals."
Frank added: "The content business is both changing rapidly and becoming more global by the day and this is a huge opportunity to be at the very heart of this revolution.
"In my opinion to succeed you need two things - brilliant creative executives and scale. This deal delivers both and I am confident that the Zodiak management team can build a world-beating company."
After being founded in 1993, RDF was floated on the stock market in 2005, but taken private again in 2009 by a consortium of RDF managers with funds managed by Cyrte Investments.
After the RDF deal, Zodiak will be approximately 71% owned by De Agostini, with the remaining 29% being held by Zodiak Managers, including RDF executives and funds managed by Cyrte.